An optical element that serves as a light-receiving element and a light-emitting element used for optical communications is optically coupled to an optical fiber or the like, which is an optical transmission medium. The optical coupling between the optical element and the optical fiber is performed using a lens.
Related art is disclosed in Japanese Laid-open Patent Publication Nos. 2000-180605, 1-178443, 2006-150751, 2006-323147, 2006-264253, or 2000-75106.